1. Field of the Invention
The present invention relates generally to force applying devices, and more particularly to apparatus for repairing a deformed, yieldable structure.
2. Description of the Prior Art
Apparatus for repairing the body of a motor vehicle which positions the vehicle on and secures it to a raised, integrated frame/platform are known. Examples of such apparatus are disclosed in U.S. Pat. Nos. 4,151,737 and 4,365,705, both of which are entitled "Apparatus for Repairing and Straightening" which issued respectively on May 1, 1979 and June 29, 1982, to Gerald A. Specktor ("the Specktor patents"), and in U.S. Pat. No. 4,313,335 entitled "Vehicle Work Rack Structure" issued Feb. 3, 1982 to Leonard F. Eck ("the Eck patent"). In each of the preceding patents, the motor vehicle is secured to the raised, integrated frame/platform while a force is applied to the vehicle from one or more vertical pull-towers secured to and locatable about the perimeter of the frame/platform.
The integrated frame/platforms which are disclosed in both the Specktor patents and the Eck patent include a plurality of apertures formed therethrough which are used in restraining the motor vehicle while a repair is being made. In the Specktor patents, the integrated frame/platform includes apertures adapted to receive a bolster which engages and restrains a frame member of a motor vehicle. Two difficulties are present with this particular technique for restraining a vehicle during repair. The first is that it requires precise positioning of the vehicle with respect to the aperture so the bolster may be properly mated with the frame member. The second is that there are a limited number of locations at which the bolster may be positioned on the apparatus. In the Eck patent, the apertures formed through the frame/platform receive and secure one end of a chain. The other end of the chain is secured to the motor vehicle. While the use ot a chain rather than a bolster to secure the motor vehicle to the integrated frame/platform relaxes the requirement for precise vehicle positioning, the vehicle is moved prior to repair relative to the frame/platform to remove slack from the chain and is moved after completing the repair relative to the frame/platform to release the tension in the chain. Further, the use of apertures formed through the frame/platform to receive one end of the chain limits the possible locations at which the chain may be secured.
The pull-towers secured to the integrated frame/platform as disclosed in the aforementioned patents employ comparatively cumbersome structures to couple a force generated by a hydraulic cylinder to a location on the motor vehicle. The Specktor patents disclose one example of a class of pull-towers in which a hydraulic cylinder is secured within the pull-tower with the movable end thereof extending out of the top of the pull-tower. An upper pulley is secured at the end of the hydraulic cylinder extending out of the top of the pull-tower. A chain is arranged in an inverted U-shaped configuration over the upper pulley and secured at one end to the pull-tower immediately beneath the pulley. From the upper pulley, the remaining portion of chain extends downwardly along one side of the pull-tower to a lower pulley. The lower pulley is mounted on a collar which surrounds the pull-tower and may be secured thereto at any vertical location along the pull-tower. Raising or 1owering the collar on the pull-tower raises or lowers the location from which a force may be applied in repairing a vehicle.
In the type of pull-tower disclosed in the Specktor patents energizing the hydraulic cylinder extends the hydraulic cylinder vertically out of the pull-tower. This action raises the upper pulley of the chain extending outwardly from the lower pulley and draws the portion toward the pull-tower. In addition to generating a force urging the portion of the chain that extends from the lower pulley to be drawn inwardly toward the pull-tower, the extension of the hydraulic cylinder also applies a substantially equal force urging the collar on which the lower pulley is mounted to rise upwardly on the pull-tower. Frequently, the collars of pull-towers of the type disclosed in the Specktor patents slip upwardly along the pull-tower while a repair is being made, because the collar must always resist a force urging it upwardly along the pull-tower which is substantially equal to the force being applied in repairing the body of a motor vehicle.
An example of a second class of pull-towers is disclosed in the Eck patent. In this second class of pull-towers, rather than raising an upper pulley located at the top of the pull-tower to couple force generated by a hydraulic cylinder to a chain, such force transfer is achieved by having the hydraulic cylinder act upon a hinged lever arm to which one end of the chain is secured. In one type of pull-towers belonging to this second class, the force applied by this hinged lever arm to the chain is applied directly to a location on a structure being repaired. The place at which the chain is attached to the hinged lever arm establishes the location from which force is applied to the vehicle. In a second type of pull-tower also belonging to this second class, the chain extending from the lever arm to the motor vehicle passes around a pulley rotatably secured on a pin inserted through a pair of holes formed through the pull-tower. A plurality of such hole pairs formed through the pull-tower permits selection of various locations from which a force may be applied to a vehicle.
There is also a third class of pull-towers in which the hydraulic cylinder extends outwardly from a collar secured about the pull-tower which collar may be moved up and down along the pull-tower. In this type of pull-tower, force generated by the hydraulic cylinder acts between the pull-tower and a yoke to which both ends of a chain are secured. The chain between the ends which are secured to the yoke extends outward therefrom on opposite sides of the pull-tower to the location on a vehicle at which force is to be applied in repairing the body. One disadvantage of this arrangement is that the hydraulic cylinder extends outwardly in an awkward manner away from the frame/platform into the space surrounding the apparatus. Another disadvantage of this arrangement is that the force generated by the pull-tower must be directed at right angles thereto. Consequently, it is possible to apply an upwardly or downwardly sloping force in repairing the body of a motor vehicle only if the pull-tower may be arranged along a sloping angle which is the complement of the direction of the desired sloping force.
In the Specktor patents, movement of the pull-towers about the perimeter of the frame/platform is achieved by rotating them in a horizontal plane about fixed axes of rotation passing through the frame/platform. Conversely, the pull-towers of the Eck patent are movable along an oval track established by the frame/platform. In the event there is failure in the structure which attaches the pull-tower to the frame/platform while repairing the body of a motor vehicle, then the pull-tower disclosed in both the Specktor patents and the Eck patent will simply fall off the respective apparatus. The possibility of such a failure may expose an operator of either apparatus to bodily injury.